Generally speaking, there are two main types of rotary engine geometries that operate within a chamber. Perhaps the simplest form is an arrangement of one or more radially projecting vanes which slide in and out or through a slotted hub on a displaced center within a circular or non-circular chamber. Vane movement is usually considerable as are the lubrication requirements, in the context of air compressor applications. While the lubrication requirements often become a nuisance, such are not insurmountable.
Another form of rotary displacement pump/motor utilizes a rotor with two, three or even four active rotor sides, the rotor orbiting and gyrating upon a reduced diameter toothed shaft. Possibly the best-known example of such rotary geometry is an internal combustion engine generally referred to as a Wankel engine. This engine operates using a triangular rotor gyrating around a figure eight-like chamber periphery. The rotor meshes onto a hollow, externally toothed shaft, a toothed bore of the rotor having a diameter significantly greater than that of the shaft. This toothed gearing operates to thrust the rotor to hoop around the shaft in a gyrating cycle within the chamber geometry. The movement causes live volume displacement between any two rotor tip faces on each of the three rotor sides. This, in turn, creates the four cycles of internal combustion at set arcs around the chamber. While useful, the motion of the rotor often causes undue wear on the rotor tips resulting in limited life. Even with this drawback and associated fuel port bypass problems, however, the Wankel engine creates enormous compact power.
At the turn of the century, a number of attempts were made to incorporate a similar chamber profile into a pump/engine. Although these arrangements were useful, the rotary component was found fundamentally flawed. In particular, the rotary component comprised a single sliding vane that slides through a rotating boss or shaft. Such arrangements, by their nature, had no facility to provide an outwardly radial seal, and required that inoperable amounts of lubricant be exposed to the chamber in order to lubricate the sliding action.
Variable delivery arrangements such as an oil pump provide a means for adjusting and controlling delivery to match engine requirements, thus improving the overall energy efficiency in engines. In general, engines require a significantly (up to about 60%) lower linear output of oil delivery per engine rotation cycle at high speed than they do at low speed. As engine speed increases therefore the oil delivery rate per engine rotation cycle must be reduced proportionately in order to balance oil flow rates to specific engine requirements.
In addition, there is a distinct imbalance between the performance of conventional gear profiled oil pumps and precise engine requirements, especially at higher speeds when pump output increases and delivery requirements per engine cycle diminish. Accordingly, excessive oil flow frequently results at high engine speeds, this excess being typically released into the sump causing significant turbulence, mist and foaming within the lower engine sector. Such excessive delivery output causes a situation by which conventional oil pump arrangements can absorb up to as much as about 4% of the engine's total power output.
The main drawbacks of existing vehicles are essentially that internal combustion engines are only around 20% efficient and electric battery vehicles are excessively heavy. Electricity is clean, and the energy prices, at off-peak are around one seventh that of petrol. Potentially, however, there are more immediate prospects of increasing efficiency of conventional vehicles by switching to external combustion. Internal combustion engines have to expel large amounts of heat energy, whereas external combustion engines actually utilize this heat. By combining this approach with a heat cell the main fuel could be pre-charged electrical heat, and there would be associated environmental benefits. The weight of a heat cell to achieve a ninety-mile range at fourteen horsepower (10kw) would be only about 200kg. The extra weight is considered inconsequential when compared to the enormous fuel cost savings and environmental benefits. Electric battery powered vehicles typically carry over 500kg of battery for half this range. Heat cell power to weight ratios would provide performance characteristics comparable to petrol vehicles. Such vehicles could be pre-charged overnight with pre-required energy levels to further maximize the efficiency of the following day's travel. It would be possible to achieve a match in conventional vehicle weights and still retain a 100kg heat cell by virtue of the reduced engine plant weight. This would create a dual fuel vehicle capable of short runs of 40 miles plus that are electric heat driven and longer runs using external combustion fueling.
With respect to the viability of the heat cell powered vehicle, detailed calculations reveal the following: while conventional re-chargeable vehicle batteries hold only about 0.01765kw hours of energy per kg, magnetite heat cells at 800° C. store about 0.149kw hours per kg. This represents an 8.4 fold benefit by weight. A 200kg heat cell would provide a vehicle range of about 90 miles at 14 horsepower (10 kw). Heat engine performance characteristics would be comparable to those of petrol vehicles. Also, heat cells have an indefinite life expectancy when compared with vehicle batteries. Fuel running costs using off-peak electricity would be 1/7th that of current petrol pricing, for instance, in the United Kingdom. In addition, a 90 mile heat cell (200 kg) would measure 450mm×450mm×450mm, or the size of a portable television (16″×16″×16″) including the casing and insulation. The heat energy retained would be about 92.7% over 18 hours and approximately 71% over 72 hours. This assumes the worse energy loss (efficiency) case scenario of a fully charged heat cell where there is no positive energy extraction within the period.